There is a world-wide twin epidemic of obesity and Type 2 Diabetes (T2D), with an urgent need to find effective new drug treatments for inducing weight loss. Stable derivatives of the endogenous glucoregulatory hormone, glucagon-like peptide-1 (GLP1) are in clinical use for the treatment of T2D but are of equally great interest as an emerging treatment of obesity and of age-related neurodegenerative conditions including Parkinson's and Alzheimer's disease. Another glucoregulatory hormone, glucose-dependent insulinotropic peptide (GIP) has recently been shown to induce a synergistic profile of metabolic and neuroprotective benefit with GLP1 in animal studies. However, for GIP to be clinically useful for any of the envisioned combination treatments, e.g. to further enhance the weight loss induced by GLP1 based medications, GIP needs to be modified to confer protection from rapid enzymatic degradation in the blood stream. The applicants (Velum, Inc.) have access to a patent-protected novel strategy to make GIP fully resistant to its main inactivation mechanism of amino- terminal enzymatic cleavage, by attaching functionally well-tolerated decorations to the peptide's first amino acid. In this phase I application, they propose to apply this strategy, in conjunction with complementary modifications to stabilize GIP, with the goal of identifying a lead compound that holds promise for future development. In collaboration with Tufts University, where biological assessment of compounds will be performed, two Specific Aims will be pursued. Starting with a prototype stable GIP analogue that has already been engineered, VEL-42, Aim 1 is to further improve on this molecule by introducing alternative amino- terminal decorations and fatty acid acylations of other selected GIP residues. A total of 12 follow-up molecules to VEL-42 will be generated. These will be tested for agonist activity/receptor potency and enzyme stability in vitro, as well as for survival in the blood stream after subcutaneous injection in mice. Serum peptide levels will be followed using a sensitive bioassay that has been developed for this project to enable compound detection regardless of structural modifications. In Aim 2, to establish efficacy in a model of therapeutic application, two analogues with highest potency and stability will be selected for studying drug-induced weight loss in mice with diet-induced obesity. As the experimental paradigm, GIP analogues will be co-injected every third day over a three week period with a latest generation GLP1-based drug, thus enabling the detection of synergistic effects on weight loss and obesity-related hyperglycemia. It is anticipated that a candidate GIP analogue will be identified that can be developed in future Phase II studies as a companion drug for GLP1 agonists for the treatment of obesity and of neurodegenerative disease.